Method for mapping ventricular/atrial premature beats during sinus rhythm

ABSTRACT

While detecting a cardiac arrhythmia, a mapping electrode of a probe is used to associate a local activation time with a first location in a region of interest in the heart. While detecting an absence of the cardiac arrhythmia, the local activation time is associated with a second location in the heart. Electrical data of the first location is assigned to the second location, and an electroanatomic map of the heart is generated that includes the second location in association with the assigned electrical data of the first location.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 14/024,859, filed Sep. 12,2013 and incorporated here by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to invasive medical devices. More particularly,this invention relates to identifying the anatomical origin ofinfrequent premature contractions of the heart chambers using aninvasive probe.

Description of the Related Art

The meanings of certain acronyms and abbreviations used herein are givenin Table 1.

TABLE 1 Acronyms and Abbreviations CL Cycle Length IS Induced Signal LATLocal Activation Time PM Pace Mapped PVC Premature VentricularContraction SR Sinus Rhythm VT Ventricular Tachycardia

Cardiac arrhythmia, such as atrial fibrillation, occurs when regions ofcardiac tissue abnormally conduct electric signals to adjacent tissue,thereby disrupting the normal cardiac cycle and causing asynchronousrhythm.

Procedures for treating arrhythmia include surgically disrupting theorigin of the signals causing the arrhythmia, as well as disrupting theconducting pathway for such signals. By selectively ablating cardiactissue by application of energy via a catheter, it is sometimes possibleto cease or modify the propagation of unwanted electrical signals fromone portion of the heart to another. The ablation process destroys theunwanted electrical pathways by formation of non-conducting lesions.

Mapping of electrical potentials in the heart is now commonly performed,using cardiac catheters comprising electrophysiological sensors formapping the electrical activity of the heart. Typically, time-varyingelectrical potentials in the endocardium are sensed and recorded as afunction of position inside the heart, and then used to map a localelectrogram or local activation time. Activation time differs from pointto point in the endocardium due to the time required for conduction ofelectrical impulses through the heart muscle. The direction of thiselectrical conduction at any point in the heart is conventionallyrepresented by an activation vector, which is normal to an isoelectricactivation front, both of which may be derived from a map of activationtime. The rate of propagation of the activation front through any pointin the endocardium may be represented as a velocity vector.

Mapping the activation front and conduction fields aids the physician inidentifying and diagnosing abnormalities, such as ventricular and atrialtachycardia and ventricular and atrial fibrillation, which result fromareas of impaired electrical propagation in the heart tissue.

Localized defects in the heart's conduction of activation signals may beidentified by observing phenomena such as multiple activation fronts,abnormal concentrations of activation vectors, or changes in thevelocity vector or deviation of the vector from normal values. Examplesof such defects include re-entrant areas, which may be associated withsignal patterns known as complex fractionated electrograms. Once adefect is located by such mapping, it may be ablated (if it isfunctioning abnormally) or otherwise treated to restore the normalfunction of the heart insofar as is possible.

Mapping of the electrical activation time in the heart muscle requiresthat the location of the sensor within the heart be known at the time ofeach measurement. In the past, such mapping was performed using a singlemovable electrode sensor inside the heart, which sensor measuredactivation time relative to a fixed external reference electrode. Thistechnique, however, requires calibration, for example impedancecalibrations with adjustments for impedance unrelated to that of thebody. Mapping of electrical activation time using a single electrodewas, furthermore, a lengthy procedure, generally performed underfluoroscopic imaging, and thereby exposing the patient to undesirableionizing radiation. Furthermore, in an arrhythmic heart, activationtimes at a single location may change between consecutive beats.

Because of the drawbacks of single-electrode mapping, a number ofinventors have taught the use of multiple electrodes to measureelectrical potentials simultaneously at different locations in theendocardium, thereby allowing activation time to be mapped more rapidlyand conveniently, as described.

A reentrant circuit that produces sinus PVC's is one pathologicalcondition amenable to ablative treatment. Identifying the optimum pointof line of ablation is a practical difficulty, even with modernelectroanatomic mapping equipment. U.S. Pat. No. 7,245,962 to Ciaccio etal. proposes a method and system for identifying and localizing areentrant circuit isthmus in a heart of a subject during sinus rhythm.The method may include (a) receiving electrogram signals from the heartduring sinus rhythm via electrodes, (b) creating a map based on theelectrogram signals, (c) determining, based on the map, a location ofthe reentrant circuit isthmus in the heart, and (d) displaying thelocation of the reentrant circuit isthmus.

U.S. Patent Application Publication No. 2009/0099468 to Thiagalingam etal. proposes locating a region of interest to ablate by recordingelectrogram data and corresponding spatial location data of an electrodethat records the electrogram data; defining at least one referencechannel containing a reference beat for determining temporal locationsand against which beats of the recorded electrogram data are compared;examining the recorded electrogram data; defining a temporal locationfor each beat of the recorded electrogram data, and creating andanalyzing an index of the temporal locations and other information ofthe beats within the recorded electrogram.

SUMMARY OF THE INVENTION

There is provided according to embodiments of the invention a method ofablation, which is carried out by inserting a probe into a heart of aliving subject, urging the mapping electrode of the probe into acontacting relationship with a target tissue in a region of interest ofthe heart, and while detecting a cardiac arrhythmia, using the mappingelectrode to associate a local activation time with a first location inthe region of interest. The method is further carried out whiledetecting an absence of the cardiac arrhythmia and maintaining thecontacting relationship, by associating the local activation time with asecond location in the heart, assigning electrical data of the firstlocation to the second location, and generating an electroanatomic mapof the heart by including at least the second location for displaythereof using the assigned electrical data of the first location.

According to an aspect of the method, detecting a cardiac arrhythmia anddetecting an absence of the cardiac arrhythmia comprise obtainingelectrocardiographic signals via the mapping electrode, holding a seriesof the electrocardiographic signals in a buffer, selecting a firstsignal from the buffer as indicative of the cardiac arrhythmia, andselecting a second signal from the buffer as indicative of the absenceof the cardiac arrhythmia.

An additional aspect of the method includes navigating an ablationelectrode to the assigned electrical data of the second location forablation thereof referencing the electroanatomic map while navigatingthe ablation electrode.

Another aspect of the method includes displaying the first location onthe electroanatomic map and excluding the first location fromcomputations in generating the electroanatomic map.

According to one aspect of the method, detecting a cardiac arrhythmiaincludes identifying premature ventricular contractions wherein a cyclelength thereof is within a predetermined range.

In a further aspect of the method, the probe has multiple mappingelectrodes and the method is carried out by acquiring multiple instancesof the first location and the second location using respective ones ofthe mapping electrodes.

Yet another aspect of the method is carried out by pace mapping anddetermining at respective locations a pace map correlation betweensignals produced during ventricular tachycardia and signals produced bypace mapping and wherein assigning electrical data includes assigningthe pace map correlation of the first location to the second location.

There is further provided according to embodiments of the invention amedical apparatus, including a probe, adapted for insertion into aheart, the probe including an elongated body, and a mapping electrodedisposed on a distal portion of the body, a memory having programsstored therein, a display, and a processor linked to the display that iscoupled to access the memory to execute the programs. The processor isconnectable to receive an input provided by the mapping electrode,wherein the programs cause the processor to perform the steps ofobtaining electrocardiographic signals from a target in the heart viathe mapping electrode, holding a series of the electrocardiographicsignals in a buffer, selecting a first signal from the buffer asindicative of a cardiac arrhythmia, the first signal occurring at afirst point in time, and selecting a second signal from the buffer asindicative of an absence of the cardiac arrhythmia, the second signaloccurring at a second point in time, associating a first localactivation time of the target at a first location of the mappingelectrode at the first point in time, associating a second localactivation time of the target at a second location of the mappingelectrode at the second point in time, assigning electrical data of thefirst location to the second location, generating an electroanatomic mapbased on the assigned electrical data at the second location, andpresenting the electroanatomic map on the display, the electroanatomicmap showing the first location and the second location.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present invention, reference is madeto the detailed description of the invention, by way of example, whichis to be read in conjunction with the following drawings, wherein likeelements are given like reference numerals, and wherein:

FIG. 1 is a pictorial illustration of a system for performing ablativeprocedures on a heart of a living subject, which is constructed andoperative in accordance with an embodiment of the invention;

FIG. 2 is a flow chart of a method of mapping arrhythmogenic areasproducing ventricular premature beats in accordance with an embodimentof the invention;

FIG. 3 is a screen display illustrating a representative localactivation time map of a heart in accordance with an embodiment of theinvention;

FIG. 4 is a screen display of a local activation time map 73illustrating points of interest, in accordance with an embodiment of theinvention;

FIG. 5 is a screen display illustrating a role of a spline catheter inthe generation of a local activation time map in accordance with anembodiment of the invention; and

FIG. 6 is a flow chart of a method of mapping arrhythmogenic areasproducing ventricular premature beats in accordance with an alternateembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the various principles ofthe present invention. It will be apparent to one skilled in the art,however, that not all these details are necessarily always needed forpracticing the present invention. In this instance, well-known circuits,control logic, and the details of computer program instructions forconventional algorithms and processes have not been shown in detail inorder not to obscure the general concepts unnecessarily.

Aspects of the present invention may be embodied in software programmingcode, which is typically maintained in permanent storage, such as acomputer readable medium. In a client/server environment, such softwareprogramming code may be stored on a client or a server. The softwareprogramming code may be embodied on any of a variety of knownnon-transitory media for use with a data processing system, such as adiskette, hard drive, electronic media or CD-ROM. The code may bedistributed on such media, or may be distributed to users from thememory or storage of one computer system over a network of some type tostorage devices on other computer systems for use by users of such othersystems.

Definitions

The term “physical coordinates” of a point refers to coordinates of apoint in the body of the subject that are determined with respect tofiducials or natural anatomic landmarks.

The term “map coordinates” of a point as used herein refers tocoordinates or a point relative to a reference point on anelectroanatomic map.

System Description

Turning now to the drawings, reference is initially made to FIG. 1,which is a pictorial illustration of a system 10 for performing ablativeprocedures on a heart 12 of a living subject, which is constructed andoperative in accordance with a disclosed embodiment of the invention.The system comprises a catheter 14, which is percutaneously inserted byan operator 16 through the patient's vascular system into a chamber orvascular structure of the heart 12. The operator 16, who is typically aphysician, brings the catheter's distal tip 18 into contact with theheart wall at an ablation target site. Optionally, Electrical activationmaps, such as local activation time maps, may then be prepared,according to the methods disclosed in U.S. Pat. Nos. 6,226,542, and6,301,496, and in commonly assigned U.S. Pat. No. 6,892,091, whosedisclosures are herein incorporated by reference. One commercial productembodying elements of the system 10 is available as the CARTO® 3 System,available from Biosense Webster, Inc., 3333 Diamond Canyon Road, DiamondBar, Calif. 91765. This system may be modified by those skilled in theart to embody the principles of the invention described herein.

Areas determined to be abnormal, for example by evaluation of theelectrical activation maps, can be ablated by application of thermalenergy, e.g., by passage of radiofrequency electrical current throughwires in the catheter to one or more electrodes at the distal tip 18,which apply the radiofrequency energy to the myocardium. The energy isabsorbed in the tissue, heating it to a point (typically about 50° C.)at which it permanently loses its electrical excitability. Whensuccessful, this procedure creates non-conducting lesions in the cardiactissue, which disrupt the abnormal electrical pathway causing thearrhythmia. The principles of the invention can be applied to differentheart chambers to treat many different cardiac arrhythmias.

The catheter 14 typically comprises a handle 20, having suitablecontrols on the handle to enable the operator 16 to steer, position andorient the distal end of the catheter as desired for the ablation. Toaid the operator 16, the distal portion of the catheter 14 containsposition sensors (not shown) that provide signals to a positioningprocessor 22, located in a console 24.

Ablation energy and electrical signals can be conveyed to and from theheart 12 through one or more ablation electrodes 32 located at or nearthe distal tip 18 via cable 34 to the console 24. Pacing signals andother control signals may be conveyed from the console 24 through thecable 34 and the electrodes 32 to the heart 12. Sensing electrodes 33,also connected to the console 24 are disposed between the ablationelectrodes 32 and have connections to the cable 34.

Wire connections 35 link the console 24 with body surface electrodes 30and other components of a positioning subsystem. The electrodes 32 andthe body surface electrodes 30 may be used to measure tissue impedanceat the ablation site as taught in U.S. Pat. No. 7,536,218, issued toGovari et al., which is herein incorporated by reference. A temperaturesensor (not shown), typically a thermocouple or thermistor, may bemounted on or near each of the electrodes 32.

The console 24 typically contains one or more ablation power generators25. The catheter 14 may be adapted to conduct ablative energy to theheart using any known ablation technique, e.g., radiofrequency energy,ultrasound energy, and laser-produced light energy. Such methods aredisclosed in commonly assigned U.S. Pat. Nos. 6,814,733, 6,997,924, and7,156,816, which are herein incorporated by reference.

The positioning processor 22 is an element of a positioning subsystem inthe system 10 that measures location and orientation coordinates of thecatheter 14.

In one embodiment, the positioning subsystem comprises a magneticposition tracking arrangement that determines the position andorientation of the catheter 14 by generating magnetic fields in apredefined working volume and sensing these fields at the catheter,using field generating coils 28. The positioning subsystem may employimpedance measurement, as taught, for example in U.S. Pat. No.7,756,576, which is hereby incorporated by reference, and in theabove-noted U.S. Pat. No. 7,536,218.

As noted above, the catheter 14 is coupled to the console 24, whichenables the operator 16 to observe and regulate the functions of thecatheter 14. Console 24 includes a processor, preferably a computer withappropriate signal processing circuits. The processor is coupled todrive a monitor 29. The signal processing circuits typically receive,amplify, filter and digitize signals from the catheter 14, includingsignals generated by the above-noted sensors and a plurality of locationsensing electrodes (not shown) located distally in the catheter 14. Thedigitized signals are received and used by the console 24 and thepositioning system to compute the position and orientation of thecatheter 14, and to analyze the electrical signals from the electrodes.

Typically, the system 10 includes other elements, which are not shown inthe figures for the sake of simplicity. For example, the system 10 mayinclude an electrocardiogram (ECG) monitor, coupled to receive signalsfrom one or more body surface electrodes, to provide an ECGsynchronization signal to the console 24. As mentioned above, the system10 typically also includes a reference position sensor, either on anexternally-applied reference patch attached to the exterior of thesubject's body, or on an internally-placed catheter, which is insertedinto the heart 12 maintained in a fixed position relative to the heart12. Conventional pumps and lines for circulating liquids through thecatheter 14 for cooling the ablation site are provided.

Application of the system 10 to the ablation of regions causingtransient arrhythmias, e.g., short runs of PVC's, presents certaintechnical difficulties. The medical procedure encompasses two stages,which may be accomplished in the same or different sessions.

In any case, in a first stage, one object is to identify a point havingthe shortest local activation time in an arrhythmogenic region of theheart, referred to herein as a “PVC point”. Typically, anelectroanatomic map is generated during the first stage. Althoughaspects of the invention are described for convenience with respect toPVC's, its principles are equally applicable to premature atrialcontractions.

In a second stage, which occurs subsequent to the first stage, ablationof tissue in a region about the PVC point is performed. This is intendedto interrupt automatic focal electrical activity and thereby preventrecurrence of the arrhythmia. In the second stage, the ablationelectrode is navigated to the PVC point, which is a location on theelectroanatomic map having the previously determined shortest localactivation time. Often, by the time ablation has been accomplished, thepatient has returned to sinus rhythm (SR). The term “sinus rhythm” isemployed herein for convenience as an example of a stable cardiacrhythm. It will be recalled that in the case of a patient withinfrequent premature ventricular contractions, the abnormal heart rateoriginating from the ventricle appears infrequently and in short bursts(1-3 beats). The heart is mostly in sinus rhythm, except that from timeto time short PVC bursts appear. When creating a map consisting of PVClocation points and their associated activation times, a discrepancylikely exists between the locations of the map's points (PVC geometry)and the navigational catheter, as the ablation catheter location isdisplayed mostly in sinus rhythm. As a result, the ablated area will notbe optimum to correct the patient's arrhythmia. It is believed that thegeometry of the heart differs during sinus rhythm, compared to itsgeometry during runs of ventricular tachycardia.

In any event, it is desirable to accurately identify the physicallocation of the PVC point subsequent to its original determination.

In embodiments of the invention, the following procedure is suitable forrecording signals during mapping: record approximately 2.5 seconds ofeach mapping electrode, and capture PVC complexes in a beat buffer,which holds and graphically displays the last few beats recorded by theelectrocardiogram. Typically, 10 beats are held in the beat buffer.Inspection of the beat buffer allows abnormal beats such as PVCs to beidentified automatically or automatically with operator assistance, ormanually by the operator. This phase may be automated according to anoperator-selected cycle length range, a procedure, which is available inthe above-noted CARTO system. Alternatively, the operator can manuallyacquire a point and the related beat buffer whenever he notices a PVCoccurrence.

Operation

Reference is now made to FIG. 2, which is a flow chart of a method ofmapping arrhythmogenic areas producing ventricular premature beats whilethe subject is in sinus rhythm, in accordance with an embodiment of theinvention. The figures described below are obtained using the CARTO 3system, and are presented for convenience. However, the method may beperformed with other imaging and mapping systems.

At initial step 37, a cardiac catheter having mapping electrodes andlocation sensors is inserted into the heart of a subject, using knownmethods. Catheters such as the PentaRay® NAV or Navistar® Thermocool®catheters, available from Biosense Webster, are suitable for use ininitial step 37. The catheter is navigated to an abnormal area 39 (FIG.3).

It is assumed that the subject is experiencing transient PVCs, eitherspontaneously occurring, or induced as noted above. The appearance of aPVC is noted at step 41.

Next, at step 43, the beat buffer is filled with PVC and SR beats, andfrozen to prevent its replacement by new beats.

The method continues with step 45. A beat showing a qualifyingelectrical abnormality, e.g., a PVC, is identified on the beat buffer.This step may be performed automatically or by the operator. Next, atstep 47, a point in the area 39, referred to for convenience as a “PVCpoint” is automatically acquired based on the beat in the beat bufferthat was chosen in step 45. Optionally, the PVC point is acquired onlyif the cycle length of the selected beat falls within a predeterminedrange. Acquisition of the point comprises (1) determining the locationthe point, typically by using a location sensor to determine theposition of the mapping electrode; (2) obtaining electrical dataregarding the point from the mapping electrode, specifically its LAT;and (3) displaying the point on a map, e.g., an LAT map.

When catheters having multiple mapping electrodes are used, e.g., splineor lasso catheters, many points may be acquired concurrently. The PVCpoint ideally has the earliest local activation time within the abnormalarea; however this is not essential; points throughout the area 39 (FIG.3) may be acquired and displayed.

Next, at step 49, a second beat (SR beat) is selected from the beatbuffer. The second beat represents normal sinus rhythm for the patient.Then, at step 51, a second point (SR point) is acquired and displayed onthe same map as the PVC point. Generally, the locations of the PVC pointand the SR point differ on the map, as explained above.

Next, at step 53, electrical information, e.g., the local activationtime (LAT) of the PVC point that was established in step 47 isassociated with the SR point in a single representative display byassigning the information to the SR point.

Next, at step 55, the PVC point is designated as “floating”, meaningthat the location of the PVC point may be indicated on LAT maps toindicate the disparity in the geometry of the heart when it isexperiencing PVCs and SR. However, the

PVC point is excluded from computations in the generation of such maps,and does not contribute to the map geometry and its electricalinformation. In consequence, a LAT map generated during sinus rhythmreflects the geometry of the heart in sinus rhythm, including thelocation of the SR point. However, the map is adjusted to associate theelectrical information of the PVC point at the location of the SR point.

Then, at step 57, the LAT map is regenerated or adjusted to reflect thenew data of the SR point. In other words, the SR map is presented withPVC electrical data. This version is referred to as a SR-PVC map. Asexplained above, the SR-PVC map reflects the geometry of the heartduring sinus rhythm, but has the activation time of the heart whileexperiencing PVCs.

Steps 41-57 may be performed concurrently using different mappingelectrodes, for example in a spline or lasso catheter. Additionally oralternatively steps 41-57 may be iterated to present multiple SR pointshaving reassigned PVC data on the map.

The procedure ends at final step 59. If appropriate, ablation may beperformed at the data-adjusted SR points with an ablation catheterdisplayed in SR locations. In such case, navigation of the ablationelectrode may be guided by the SR-PVC map prepared in step 57.

EXAMPLES

Reference is now made to FIG. 3, which is a screen display 61illustrating a representative local activation time map 63 of a heart 65taken during performance of step 43, in accordance with an embodiment ofthe invention. The procedure for generating a local activation time mapusing a mapping catheter is known, and therefore its details are notdiscussed herein. Local activation times are typically coded usingpseudocolor. In FIG. 3, local activation times information is codedusing patterns in accordance with a key 67. These patterns simulate thepseudocolors of an actual functional map. The area 39 has a relativelyshort LAT, and may be automatically flagged or selected by an operatoras abnormal. The area 39 is circumscribed by an area 69 that has arelatively longer local activation time.

Reference is now made to FIG. 4, which is a screen display 71 of a localactivation time map 73 illustrating points of interest, in accordancewith an embodiment of the invention. The map 73 shows the locations ofPVC point 75 and SR point 77 that were obtained according to theprocedure described above in reference to FIG. 2. The points 75, 77 areenclosed by circles for improved visibility. The beats selected from thebeat buffer in order to acquire the points 75, 77 are shown in rightpane 79 with a window of interest interval 81. The right pane 79 alsoshows the activation times of the PVC point 75 and SR point 77 on ascale 83 in the lower right portion. The beats selected are the SR andPVC points indicated by circles 85, 87, respectively. In other words,isochronal points are acquired from an area of interest using the beatbuffer during PVCs (step 45) and during sinus rhythm (step 49) are shownon the map 73 as the points 75, 77 respectively. The points 75, 77 weremeasured at different times, based on different beats in the beatbuffer, and thus are associated with different time stamps. It isevident that they have different map locations. In particular, the LATmap displays the physical coordinates of an SR point whose associatedactivation time data was obtained at a different time.

Reference is now made to FIG. 5, which is a screen display 89illustrating a role of a spline catheter in the generation of a localactivation time map 91, in accordance with an embodiment of theinvention.

A spline catheter 93, e.g., the above noted Pentaray NAV catheter hasbeen navigated such that an electrode of one of the spline, spline 95 isin contact with a point on a colored area 97, which has anomalous shortactivation times throughout. By appropriate repositioning of the splinecatheter 93, PVC and SR points may then be automatically acquired usingone or more splines, and processed according to the method describedabove with reference to FIG. 2.

Alternate Embodiment

Another embodiment of the invention involves pace mapping, for exampleusing PaSo™ software.

Pace mapping is a diagnostic technique used for identification ofventricular tachycardia foci. This involves pacing the chamber at theventricular tachycardia rate, then comparing a body surface 12 -lead ECGacquired during pacing to an ECG recorded during clinical arrhythmia,either induced or previously recorded.

In this embodiment, the mapping phase is used to identify a pace-mapcorrelation, i.e., a correlation between signals produced duringventricular tachycardia and signals produced by pace mapping, referredto as pace mapped—induced signal (PM-IS) correlation, as taught incommonly assigned U.S. Pat. No. 7,907,994 to Stolarski et al., which isherein incorporated by reference. A paced rhythm point serves as the PVCpoint from which PVC's originate. A map produced during pacing functionsin the same manner as the map produced during sinus rhythm in theprevious embodiment.

Reference is now made to FIG. 6, which is a flow chart of a method ofmapping arrhythmogenic areas producing ventricular premature beats whilethe subject is in sinus rhythm, in accordance with the precedingalternate embodiment of the invention. Some of the steps in FIG. 6 areperformed in the same manner as those of FIG. 2. Their description isnot repeated in the interest of brevity.

After performing initial step 37, pacing is conducted at step 99. Apoint is then acquired at step 101, and pacing is then discontinued atstep 103.

Next, at step 105, the beat buffer is filled with pace-mapped (PM) beatsand SR beats.

Next, at step 107, a PM beat is selected from the beat buffer.

Then, after performing steps 47, 49 and 51 as described above, at step109, the pace-mapped correlation based on the PM point acquired in step47 is assigned to the SR point location that was selected in step 51.

Next, at step 111, the PM point is presented as floating.

Next, at step 113, the SR Map is presented with PM-IS correlation data,referred to as a SR-PM map.

Then, at final step 115, ablation is performed according to the SR-PMmap.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and sub-combinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

1. A method of ablation, comprising the steps of: inserting a probe intoa heart of a living subject, the probe having a mapping electrode;urging the mapping electrode into a contacting relationship with atarget tissue in a region of interest of the heart; while detecting acardiac arrhythmia using the mapping electrode to associate a localactivation time with a first location in the region of interest; whiledetecting an absence of the cardiac arrhythmia and maintaining thecontacting relationship, associating the local activation time with asecond location in the heart; assigning electrical data of the firstlocation to the second location; and generating an electroanatomic mapof the heart by including at least the second location for displaythereof using the assigned electrical data of the first location.
 2. Themethod according to claim 1, wherein detecting a cardiac arrhythmia anddetecting an absence of the cardiac arrhythmia comprise: obtainingelectrocardiographic signals via the mapping electrode; holding a seriesof the electrocardiographic signals in a buffer; selecting a firstsignal from the buffer as indicative of the cardiac arrhythmia; andselecting a second signal from the buffer as indicative of the absenceof the cardiac arrhythmia.
 3. The method according to claim 1, furthercomprising the steps of: navigating an ablation electrode to theassigned electrical data of the second location for ablation thereofreferencing the electroanatomic map while navigating the ablationelectrode.
 4. The method according to claim 3, further comprising thestep of displaying the first location on the electroanatomic map andexcluding the first location from computations in the step of generatingthe electroanatomic map.
 5. The method according to claim 1, whereindetecting a cardiac arrhythmia comprises identifying prematureventricular contractions wherein a cycle length thereof is within apredetermined range.
 6. The method according to claim 1, wherein theprobe has multiple mapping electrodes, further comprising acquiringmultiple instances of the first location and the second location usingrespective ones of the mapping electrodes.
 7. The method according toclaim 1, wherein using the mapping electrode comprises pace mapping,further comprising determining at respective locations a pace mapcorrelation between signals produced during ventricular tachycardia andsignals produced by pace mapping and wherein assigning electrical datacomprises assigning the pace map correlation of the first location tothe second location.